The present invention disclosed herein relates to a photodetector and a method of fabricating the same, and more particularly, to a germanium photodetector and a method of fabricating the same.
Recent silicon-based optical communication technology uses germanium in both of the active device and passive device applications. Because the band gap energy (0.67 eV) of the germanium is smaller than the band gap energy (1.12 eV) of the silicon, the germanium can detect generic optical communication wavelengths λ of 1.3 μm to 1.6 μm that cannot be detected by the silicon. However, the germanium has a lattice constant difference of 4% from the silicon. Therefore, it is difficult to grow a low-defect germanium epitaxial layer directly on a silicon substrate. There is a method of fabricating a p-i-n detector by forming a SiGe buffer layer between the silicon substrate and the germanium epitaxial layer. However, the buffer layer has many inherent crystal defects, and the buffer layer must be thick enough to grow the germanium epitaxial layer. Therefore, the buffer layer degrades the detector's performance and also imposes many restrictions on the fabrication process. There is a method of forming the germanium epitaxial layer on the silicon substrate through an ultra-high vacuum process of 10−9 torr or less, such as ultra-high vacuum chemical vapor deposition (UHVCVD) or molecular beam epitaxy (MBE), without using the buffer layer. This method, however, requires a high-temperature annealing process of 700° C. or more in order to reduce crystal defects such as dislocations. Thus, due to the high-temperature annealing process, the method is low in productivity and has a limitation in mass production.